DEVELOPMENT OF ELASMOBRAXCH FISHES. 237 



Instead of all the brandies from the ring being of nearly 

 equal size, two of them are especially developed. The venous 

 system has undergone no important changes. 



In fig. 5 the circulation is represented at a still later stage. 

 The arterial ring has come to embrace the whole yolk, and as 

 a result of this, has in its turn vanished as did the venous ring 

 before it. At this stage of the circulation there is present a 

 single arterial and a single venous trunk. The arterial trunk is 

 a branch of the dorsal aorta, and the venous trunk originally 

 falls into the heart together with the subintestinal or splanch- 

 nic vein, but on the formation of the liver enters this and 

 breaks up into capillaries in it. The venous trunk leaves the 

 body on the right side, and the arterial on the left. 



The most interesting point to be noticed in connection 

 with the yolk-sack circulation of Scyllium is the fact of its 

 being formed on a completely different type to that of the 

 Amniotic Vertebrates. 



The Vascular Glands. 



There are in Scyllium two structures which have gone 

 under the name of the suprarenal body. The one of these 

 is an unpaired rod-like body lying between the dorsal aorta 

 and the caudal vein in the region of the posterior end of the 

 kidneys. This body I propose to call the inter^renal body. The 

 other is formed by a series of paired bodies situated dorsal to 

 the cardinal veins on branches of the aorta, and arrano^ed 

 segmentally. These bodies I shall call the suprarenal bodies. 

 I propose treating the literature of these bodies together, since 

 they have usually been dealt w^ith in this way, and indeed re- 

 garded as parts of the same system. As I hope to shew in 

 the sequel, the origin of these bodies is very different. The 

 interrenal body appears to be developed from the mesoblast ; 

 w^hile my researches on the suprarenal bodies confirm the 

 brilliant investigations of Leydig, shewing that they are formed 

 out of the sympathetic ganglia. 



The most important investigations on these bodies have 

 been made by Leydig\ In his first researches, Bochen u. Haie, 



1 Rochen und Hale and Uiitersuchung. U. Fische u. Bcptilien. 



